This invention relates to systems for optical imaging in wide-field epiflourescence microscopy, and particularly to the use of an optical pathway selector that directs a beam of light propagating along a first optical axis to propagate along a different optical axis, or directs several beams of light propagating along different optical axes to propagate along a single optical axis.
In the field of epifluorescence microscopy biochemical material samples that have been tagged with fluorescent markers are exposed to a beam of light that excites markers within the samples to fluoresce. The wavelength of the fluorescence light emitted from the sample depends on the markers that have been used with the sample. Typically, fluorescence light emitted from the sample is imaged onto an image detector, such as a CCD array or image tube in a camera, or is scanned point-by-point onto a detector whose output is processed by software, in order to determine the spatial distribution of emitted fluorescence light intensity. It is often desirable to use multiple excitation light sources, each producing a different wavelength of light, to excite a given sample. Therefore, it is necessary to be able to direct light from different sources toward the sample and to direct the resulting fluorescence light toward one or more detectors.
U.S. Pat. No. 4,795,256 employs a reflective chopper to chop light from a laser so that the light propagates along two alternative optical pathways. A monochromator is disposed in each of the optical pathways to filter out two respective excitation wavelengths. However, this arrangement is limited in that it does not provide for switching between one and several bidirectional optical pathways so as to excite an epifluorescence sample with more than two wavelengths of light and detect the fluorescence light emitted therefrom.
Consequently, there is a need to be able to switch between two or more light sources and direct them toward a given sample. In addition, there is a need to direct both the excitation and emitted fluorescence light along a selected one of a plurality of bidirectional pathways.
The aforementioned need has been met in the present invention by providing an optical pathway selector having a first direction selector, a second direction selector, and an actuator. In two embodiments, the first direction selector is comprised of a substantially planar member having alternating reflecting and transparent portions. The first direction selector is disposed on an axle with the substantially planar member positioned askew to an optical axis, preferably 45 degrees. When the axle rotates so does the substantially planar member. The second direction selector has a configuration similar to that of the first direction selector. The second direction selector is mounted on the same axle and is coaxial with the first direction selector. The reflective surfaces are preferably perpendicular to the axle. Additional direction selectors can be employed in a similar manner. A motor is connected to the axle for rotating the direction selectors. In a third alternative embodiment, a motor moves the direction selector along a linear pathway in and out of the pathway of different light beams.
When a light beam propagates along a first optical axis, the first direction selector may be inserted into its pathway. The light beam either hits the reflective portion and propagates along a second optical pathway or passes through the transparent portion and continues along the first optical pathway. If the light beam continues along the first optical pathway, the second direction selector may be inserted into the pathway. The light beam either hits the reflective portion of the second direction selector and propagates along a third optical pathway, or passes through the transparent portion and continues along the first optical pathway. Additional direction selectors disposed on the axle of the optical pathway selector can be utilized in a similar manner.
Conversely, the optical pathway selector can be utilized to direct two or more light beams propagating along different optical pathways to propagate along the same optical pathway.
In another embodiment of the invention the reflective surfaces can be comprised of wave-length selective mirrors to filter out a desired wavelength of light.
In an additional embodiment of the invention, a retroreflector is utilized in conjunction with the optical pathway selector to eliminate angular path variations. The retroreflector returns a light beam that has been reflected from the optical pathway selector at the same angle that it was reflected, so that when it returns to the optical pathway selector it is reflected along a pathway that is parallel and opposite to its original pathway.
In an embodiment directed to a specific application, the optical pathway selector is used in an epifluorescence microscope.
Accordingly, it is a principal object of the present invention to provide a novel and improved method and apparatus for directing a beam of light along a selected optical pathway.
It is another object of the invention to provide a method and apparatus for directing a beam of light along a selected one of a plurality of alternative pathways.
It is a further object of the invention to provide a method and apparatus for selectively directing multiple beams of light along a single pathway.
It is yet another object of the present invention to provide a method and apparatus for switching a beam of light between one and several bidirectional pathways.
The foregoing and other objects, features, and advantages of the invention will be more readily understood upon consideration of the following detailed description of the invention, taken in conjunction with the accompanying drawings.